Abstract:

 In contrast to the present backdrop of fracture prediction mainly centering on the aperture, density and development of fracture with semiquantitative and quantitative methods and less on extension law and penetrability, the paper, taking X oilfield as an example, adopts the stress field simulation to establish relationship between stress field and fracture parameters, then to research the extension law and penetrability of sandstone fractures into mudstone. Simulated result shows that the sandstone with thin thickness is easy to produce fractures, but the thickness of sandstone has little impact on extension distance and porosity of fractures in mudstone, which even can be neglected; that is to say, whatever the thickness of sandstone above or below the mudstone is, the porosity of fractures stretching into mudstone changes little, at about 0.38%. At the same time, fracture extension length at point of contact between sandstone and mudstone falls between 15—2 m; as mudstone thickness reaches 4 m, the fracture just can not penetrate through the mudstone， here the mudstone is thick enough to act as an effective cap formation.

Key words:  sandmud interbed formation, fracture, extension law, penetrability, structural stress field